Electrochromic device with two thin glass elements and a gelled electrochromic medium

ABSTRACT

An electrochromic device comprising: a first glass element having an electrically conductive material associated therewith, wherein said first element comprises a height (h 1 ), a width (w 1 ), a thickness (t 1 ), an inner surface, and an outer surface; a second element having an electrically conductive material associated therewith, wherein said second element comprises a height (h 2 ), a width (w 2 ) , and a thickness (t 2 ), an inner surface, and an outer surface; a cell spacing (c) which comprises a distance between said inner surface of said first element and said inner surface of said second element; a gelled electrochromic medium contained within a chamber positioned between said first and second elements; wherein (h 1 ), (w 1 ), (t 1 ), (h 2 ), (w 2 ), (t 2 ), and (c) are numerical values in millimeters; and wherein (h 1 ), (w 1 ), and (t 1 ) of said first element, and (h 2 ), (w 2 ), and (t 2 ) of said second element and (c) comprise numerical values such that the following inequality is satisfied:              2          h   1   5          (     1   -          -     2       (       h   1     /     w   1       )     2             )             t   1   3          (     7.57   ×     10   12       )         +       2          h   2   5          (     1   -          -     2       (       h   2     /     w   2       )     2             )             t   2   3          (     7.57   ×     10   12       )           ≥     .1          (   c   )     .

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation-in-part of U.S. application Ser. No.09/560,849, filed Apr. 28, 2000, now U.S. Pat. No. 6,268,950, which is acontinuation of U.S. application Ser. No. 09/375,136, filed Aug. 16,1999, now U.S. Pat. No. 6,057,956, which is a continuation of U.S.application Ser. No. 08/834,783, filed Apr. 2, 1997, now U.S. Pat. No.5,940,201.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to an electrochromic devicehaving two thin glass elements and a free-standing gel, and moreparticularly, to a lightweight electrochromic device having afree-standing gel that cooperatively interacts with two thin glasselements to form a thick, strong unitary member which is resistant toflexing, warping, bowing, shattering and/or scattering.

2. Background Art

Heretofore, various automatic rearview mirrors for motor vehicles havebeen devised which automatically change from the full reflectance (day)mode to the partial reflectance (night) mode(s) for glare protectionpurposes from light emanating from the headlights of vehiclesapproaching from the rear. The electrochromic mirrors disclosed in U.S.Pat. No. 4,902,108, entitled “Single-Compartment, Self-Erasing,Solution-Phase Electrochromic Devices Solutions for Use Therein, andUses Thereof”, issued Feb. 20, 1990, to H. J. Byker; Canadian Patent No.1,300,945, entitled “Automatic Rearview Mirror System for AutomotiveVehicles”, issued May 19, 1992, to J. H. Bechtel et al.; U.S. Pat. No.5,128,799, entitled “Variable Reflectance Motor Vehicle Mirror”, issuedJul. 7, 1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled“Electro-Optic Device”, issued Apr. 13, 1993, to H. J. Byker et al.;U.S. Pat. No. 5,204,778, entitled “Control System For Automatic RearviewMirrors”, issued Apr. 20, 1993 to J. H. Bechtel; U.S. Pat. No.5,278,693, entitled “Tinted Solution-Phase Electrochromic Mirrors”,issued Jan. 11, 1994, to D. A. Theiste et al.; U.S. Pat. No. 5,280,380,entitled “UV-Stabilized Compositions and Methods”, issued Jan. 18, 1994,to H. J. Byker; U.S. Pat. No. 5,282,077, entitled “Variable ReflectanceMirror”, issued Jan. 25, 1994, to H. J. Byker; U.S. Pat. No. 5,294,376,entitled “Bipyridinium Salt Solutions”, issued Mar. 15, 1994, to H. J.Byker; U.S. Pat. No. 5,336,448, entitled “Electrochromic Devices withBipyridinium Salt Solutions”, issued Aug. 9, 1994, to H. J. Byker; U.S.Pat. No. 5,434,407, entitled “Automatic Rearview Mirror IncorporatingLight Pipe”, issued Jan. 18, 1995, to F. T. Bauer et al.; U.S. Pat. No.5,448,397, entitled “Outside Automatic Rearview Mirror for AutomotiveVehicles”, issued Sep. 5, 1995, to W. L. Tonar; and U.S. Pat. No.5,451,822, entitled “Electronic Control System”, issued Sep. 19, 1995,to J. H. Bechtel et al., each of which patents is assigned to theassignee of the present invention and the disclosures of each of whichare hereby incorporated herein by reference, are typical of modern dayautomatic rearview mirrors for motor vehicles. Such electrochromicmirrors may be utilized in a fully integrated inside/outside rearviewmirror system or as an inside or an outside rearview mirror system. Ingeneral, in automatic rearview mirrors of the types disclosed in theabove-referenced U.S. Patents, both the inside and the outside rearviewmirrors are comprised of a relatively thin electrochromic mediumsandwiched and sealed between two glass elements.

In most cases, when the electrochromic medium which functions as themedia of variable transmittance in the mirrors is electricallyenergized, it darkens and begins to absorb light, and the more light theelectrochromic medium absorbs the darker or lower in reflectance themirror becomes. When the electrical voltage is decreased to zero, themirror returns to its clear or substantially clear high reflectancestate. In general, the electrochromic medium sandwiched and sealedbetween the two glass elements is comprised of solution-phase,self-erasing system of electrochromic materials, although otherelectrochromic media may be utilized, including an approach wherein atungsten oxide electrochromic layer is coated on one electrode with asolution containing a redox active material to provide the counterelectrode reaction. When operated automatically, the rearview mirrors ofthe indicated character generally incorporate light-sensing electroniccircuitry which is effective to change the mirrors to the dimmedreflectance modes when glare is detected, the sandwiched electrochromicmedium being activated and the mirror being dimmed in proportion to theamount of glare that is detected. As glare subsides, the mirrorautomatically returns to its normal high reflectance state without anyaction being required on the part of the driver of the vehicle.

The electrochromic medium is disposed in a sealed chamber defined by atransparent front glass element, a peripheral edge seal, and a rearmirror element having a reflective layer, the electrochromic mediumfilling the chamber. Conductive layers are provided on the inside of thefront and rear glass elements, the conductive layer on the front glasselement being transparent while the conductive layer on the rear glasselement may be transparent or the conductive layer on the rear glasselement may be semi-transparent or opaque and may also have reflectivecharacteristics and function as the reflective layer for the mirrorassembly. The conductive layers on both the front glass element and therear glass element are connected to electronic circuitry which iseffective to electrically energize the electrochromic medium to switchthe mirror to nighttime, decreased reflectance modes when glare isdetected and thereafter allow the mirror to return to the daytime, highreflectance mode when the glare subsides as described in detail in theaforementioned U.S. Patents. For clarity of description of such astructure, the front surface of the front glass element is sometimesreferred to as the first surface, and the inside surface of the frontglass element is sometimes referred to as the second surface. The insidesurface of the rear glass element is sometimes referred to as the thirdsurface, and the back surface of the rear glass element is sometimesreferred to as the fourth surface.

Recently, electrochromic mirrors have become common on the outside ofvehicles, and suffer from the fact that they are significantly heavierthan standard outside mirrors. This increased weight with electrochromicmirrors exerts a strain on the mechanisms used to automatically adjustthe position of the outside mirrors. One method of decreasing the weightof an electrochromic mirror is by reducing the thickness of both glasselements or even remove one glass plate. For example, in solid stateelectrochromic devices, such as those described in U.S. Pat. No4,973,141 to Baucke et al., where all the components comprise solidstate elements, e.g., solid state electrochromic layers (WO₃ and MoO₃),solid, hydrogen ion-conducting layers, etc., it has been proposed thatthe back plate is optional. This is possible because the other layersare all in the solid phase and remain attached to the front plate. Inelectrochromic devices containing at least one solution-phaseelectrochromic material on the other hand, it is not possible to removeone glass plate because the solvent and electrochromic material wouldleak out. Therefore, the only option for electrochromic devicescontaining a solution is to decrease the glass thickness. Unfortunately,as the thickness is decreased the individual glass elements becomefragile and flexible and remain that way during and after themanufacture of an electrochromic mirror. This is especially true as themirrors become larger such as is needed on vehicles like sport-utilityvehicles and very large trucks, e.g., tractor-trailers. It is thereforedifficult to produce a commercially desirable electrochromic mirrorcontaining at least one solution-phase electrochromic material that hastwo thin glass elements because each thin glass element will be muchmore likely to flex, warp, bow and/or shatter. Properties of asolution-phase electrochromic device, such as coloring and clearingtimes and optical density when colored, are dependent on the thicknessof the electrochromic layer (e.g., the spacing between the two glasselements). Maintaining uniform spacing is necessary to maintain uniformappearance. The spacing between thin glass elements can be easilychanged even after device manufacture by applying subtle pressure on oneof the glass plates. This creates an undesirable non-uniformity in theappearance of the device.

Consequently, it is desirable to provide an improved electrochromicdevice, such as an electrochromic mirror, window, etc, having afree-standing gel containing at least one solution-phase electrochromicmaterial, where the gel cooperatively interacts with two thin glasselements to form a thick, strong unitary member which is resistant toflexing, warping, bowing, shattering and/or scattering and helpsmaintain uniform spacing between the thin glass elements.

OBJECTS OF THE INVENTION

Accordingly, a primary object of the present invention is to provide alightweight electrochromic device having a free-standing gel containingat least one solution-phase electrochromic material, where the gelcooperatively interacts with two thin glass elements to form a thick,strong unitary member which is resistant to flexing, warping, bowing,shattering and/or scattering.

Another object of the present invention is to provide a lightweightelectrochromic device having two thin glass elements that exhibitsreduced vibration, distortion and double imaging.

SUMMARY OF THE INVENTION

The above and other objects, which will become apparent from thespecification as a whole, including the drawings, are accomplished inaccordance with the present invention by providing an electrochromicdevice with thin front and rear spaced glass elements. A layer oftransparent conductive material may be placed onto the second surface,and either another layer of transparent conductive material or acombined reflector/electrode may be placed onto the third surface. Achamber is defined by the layers on the interior surfaces of the frontand rear glass elements and a peripheral sealing member. In accordancewith the present invention, the chamber contains a free-standing gelcomprising a solvent and a crosslinked polymer matrix, and furthercontains at least one electrochromic material in solution with thesolvent and interspersed in the crosslinked polymer matrix, where thegel cooperatively interacts with the thin glass elements to form athick, strong unitary member which is resistant to flexing, warping,bowing, shattering and/or scattering, and further allows the mirror toexhibit reduced vibration, distortion and double imaging.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the concluding portion of thespecification. The invention, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawings, wherelike numerals represent like components, in which:

FIG. 1 is a front elevational view schematically illustrating aninside/outside electrochromic device for motor vehicles where the insideand outside mirrors incorporate the mirror assembly of the presentinvention; and

FIG. 2 is an enlarged cross-sectional view of the inside electrochromicdevice incorporating a free-standing gel cooperatively interacting withtwo thin glass elements illustrated in FIG. 1, taken on the line 2-2′thereof.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a front elevational view schematically illustrating aninside mirror assembly 110 and two outside rearview mirror assemblies111 a and 111 b for the driver-side and passenger-side, respectively,all of which are adapted to be installed on a motor vehicle in aconventional manner and where the mirrors face the rear of the vehicleand can be viewed by the driver of the vehicle to provide a rearwardview. Inside mirror assembly 110, and outside rearview mirror assemblies111 a and 111 b may incorporate light-sensing electronic circuitry ofthe type illustrated and described in the above-referenced CanadianPatent No. 1,300,945; U.S. Pat. No. 5,204,778; or U.S. Pat. No.5,451,822, and other circuits capable of sensing glare and ambient lightand supplying a drive voltage to the electrochromic element. Mirrorassemblies 110, 111 a and 111 b are essentially identical in that likenumbers identify components of the inside and outside mirrors. Thesecomponents may be slightly different in configuration but function insubstantially the same manner and obtain substantially the same resultsas similarly numbered components. For example, the shape of the frontglass element of inside mirror 110 is generally longer and narrower thanoutside mirrors 111 a and 111 b. There are also some differentperformance standards placed on inside mirror 110 compared with outsidemirrors 111 a and 111 b. For example, inside mirror 110 generally, whenfully cleared, should have a reflectance value of about 70 percent toabout 80 percent or higher whereas the outside mirrors often have areflectance of about 50 percent to about 65 percent. Also, in the UnitedStates (as supplied by the automobile manufacturers), the passenger-sidemirror 111 b typically has a spherically bent, or convex shape, whereasthe driver-side mirror 111 a, and inside mirror 110 presently must beflat. In Europe the driver-side mirror 111 a is commonly flat oraspheric, whereas the passenger-side mirror 111 b has a convex shape. InJapan both mirrors have a convex shape. The following description isgenerally applicable to all mirror assemblies of the present invention.

Rearview mirrors embodying the present invention preferably include abezel 144, which extends around the entire periphery of each individualassembly 110, 111 a and/or 111 b. The bezel 144 conceals and protectsthe spring clips (not shown) and the peripheral edge portions of sealingmember and both the front and rear glass elements (described below). Awide variety of bezel designs are well known in the art, such as, forexample the bezel taught and claimed in above-referenced U.S. Pat. No.5,448,397. There are also a wide variety of housing well known in theart for attaching the mirror assembly 110 to the inside front windshieldof an automobile, or for attaching the mirror assemblies 111 a and 111 bto the outside of an automobile. A preferred housing for attaching aninside assembly is disclosed in above-referenced U.S. Pat. No.5,337,948.

The electrical circuit preferably incorporates an ambient light sensor(not shown) and a glare light sensor 160, the glare light sensor beingpositioned either behind the mirror glass and looking through a sectionof the mirror with the reflective material completely or partiallyremoved, or the glare light sensor can be positioned outside thereflective surfaces, e.g., in the bezel 144. Additionally, an area orareas of the electrode and reflector, such as 146 or the area alignedwith sensor 160, may be completely removed, or partially removed in, forexample, a dot or line pattern, to permit a vacuum fluorescent display,such as a compass, clock, or other indicia, to show through to thedriver of the vehicle. Co-filed U.S. patent application entitled “ANINFORMATION DISPLAY AREA ON ELECTROCHROMIC MIRRORS HAVING A THIRDSURFACE REFLECTOR” shows a presently preferred line pattern. The presentinvention is also applicable to a mirror which uses only one video chiplight sensor to measure both glare and ambient light and which isfurther capable of determining the direction of glare. An automaticmirror on the inside of a vehicle, constructed according to thisinvention, can also control one or both outside mirrors as slaves in anautomatic mirror system.

FIG. 2 shows a cross-sectional view of mirror assembly 110 along theline 2-2′. Mirror 110 has a front transparent element 112 having a frontsurface 112 a and a rear surface 112 b, and a rear element 114 having afront surface 114 a and a rear surface 114 b. Since some of the layersof the mirror are very thin, the scale has been distorted for pictorialclarity. Also, for clarity of description of such a structure, thefollowing designations will be used hereinafter. The front surface ofthe front glass element will be referred to as the first surface and theback surface of the front glass element as the second surface. The frontsurface of the rear glass element will be referred to as the thirdsurface, and the back surface of the rear glass element as the fourthsurface. Chamber 116 is defined by one or more layers of transparentconductive material 118 (disposed on front element rear surface 112 b),another layer disposed on rear element front surface 114 a comprisingeither a transparent conductive material 120 or a combinationreflector/electrode, and an inner circumferential wall 121 of sealingmember 122. Typically electrochromic mirrors are made with glasselements having a thickness of about 2.3 mm. The preferred thin glasselements according to the present invention have thicknesses of about1.0 mm, which results in a weight savings of more than 50%. Thisdecreased weight ensures that the mechanisms used to manipulate theorientation of the mirror, commonly referred to as carrier plates, arenot overloaded and further provides significant improvement in thevibrational stability of the mirror. As will be discussed in greaterdetail below, the preferred thickness of the elements can vary greatlydepending upon, among other things, the associated geometricconfiguration (i.e. the width and height) of the elements.

Front transparent element 112 may be any material which is thin andtransparent and has sufficient strength to be able to operate in theconditions, e.g., varying temperatures and pressures, commonly found inthe automotive environment. Front element 112 may comprise any type ofglass, borosilicate glass, soda lime glass, float glass or any othermaterial, such as, for example, a polymer or plastic, that istransparent in the visible region of the electromagnetic spectrum. Forpurposes of the present example, front element 112 is preferably a sheetof glass with a thickness ranging from approximately 0.5 mm toapproximately 1.5 mm. More preferably front element 112 has a thicknessranging from approximately 0.8 mm to approximately 1.2 mm, with thepresently most preferred thickness about 1.0 mm—for a small areaelectrochromic mirror. Rear element 114 must meet the operationalconditions outlined above, except that it does not need to betransparent, and therefore may comprise polymers, metals, glass,ceramics, and preferably is a sheet of glass with a thickness in thesame ranges as element 112.

When both glass elements are made thin the vibrational properties of aninterior or exterior mirror improve—although the effects are moresignificant for exterior mirrors. These vibrations, that result from theengine running and/or the vehicle moving, affect the rearview mirror,such that the mirror essentially acts as a weight on the end of avibrating cantilever beam. This vibrating mirror causes blurring of thereflected image that is a safety concern as well as a phenomenon that isdispleasing to the driver. As the weight on the end of the cantileverbeam (i.e., the mirror element attached to the carrier plate on theoutside mirror or the mirror mount on the inside mirror) is decreasedthe frequency at which the mirror vibrates increases. If the frequencyof the mirror vibration increases to around 60 Hertz the blurring of thereflected image is not visually displeasing to the vehicle occupants.Moreover, as the frequency at which the mirror vibrates increases thedistance the mirror travels while vibrating decreases significantly.Thus, by decreasing the weight of the mirror element the complete mirrorbecomes more vibrationally stable and improves the ability of the driverto view what is behind the vehicle. For example, an interior mirror withtwo glass elements having a thickness of 1.1 mm has a first modehorizontal frequency of about 55 Hertz whereas a mirror with two glasselements of 2.3 mm has a first mode horizontal frequency of about 45Hertz. This 10 Hertz differences produces a significant improvement inhow a driver views a reflected image.

No electrochromic mirrors and/or devices incorporating two thin glasselements and containing a solution-phase electrochromic material havebeen commercially available because thin glass suffers from beingflexible and therefore is prone to warping, flexing and bowing,especially when exposed to extreme environments. Thus, in accordancewith the present invention, chamber 116 contains a free-standing gelthat cooperatively interacts with thin glass elements 112 and 114 toproduce a mirror that acts as one thick unitary member rather than twothin glass elements held together only by a seal member. Infree-standing gels, which contain a solution and a cross-linked polymermatrix, the solution is interspersed in a polymer matrix and continuesto function as a solution. Also, at least one solution-phaseelectrochromic material is in solution in the solvent and therefore aspart of the solution is interspersed in the polymer matrix (thisgenerally being referred to as “gelled electrochromic medium” 124). Thisallows one to construct a rearview mirror or other electrochromic devicewith thinner glass in order to decrease the overall weight of the mirrorwhile maintaining sufficient structural integrity so that the mirrorwill survive the extreme conditions common to the automobileenvironment. This also helps maintain uniform spacing between the thinglass elements which improves uniformity in the appearance (e.g.,coloration) of the mirror. This structural integrity results because thefree-standing gel, the first glass element 112, and the second glasselement 114, which individually have insufficient strengthcharacteristics to work effectively in an electrochromic mirror, couplein such a manner that they no longer move independently but act as onethick unitary member. This stability includes, but is not limited to,resistance to, flexing, warping, bowing and breaking, as well asimproved image quality of the reflected image, e.g., less distortion,double image, color uniformity and independent vibration of each glasselement. However, while it is important to couple the front and rearglass elements, it is equally important (if not more so) to ensure thatthe electrochromic mirror functions properly. The free-standing gel mustbond reasonably well to the electrode layers (including thereflector/electrode if the mirror has a third surface reflector) on thewalls of such a device, but not substantially interfere with theelectron transfer between the electrode layers and the electrochromicmaterial(s) disposed in the chamber 116. Further, the gel must notmaterially shrink, craze or weep over time such that the gel itselfcauses poor image quality. Ensuring that the free-standing gel bondswell enough to the electrode layers to couple the front and rear glasselements and does not deteriorate over time, while allowing theelectrochromic reactions to take place as though they were in solutionis an important aspect of the present invention.

It will be understood that in addition to a solution-phaseelectrochromic medium, a hybrid electrochromic medium is likewisecontemplated for use. In a hybrid electrochromic medium, one of thecathodic or anodic materials can be applied (in a solid form) to itsrespective electrically conductive or semi-conductive material. Forexample, tungsten oxide (WO₃) or polyaniline can be applied onto thesurface of a conventional electrically conductive material.Additionally, numerous viologens can be applied onto, among othermaterials, TiO₂.

To perform adequately a mirror must accurately represent the reflectedimage, and this cannot be accomplished when the glass elements (to whichthe reflector is attached) tend to bend or bow while the driver isviewing the reflected image. The bending or bowing occurs mainly due topressure points exerted by the mirror mounting and adjusting mechanismsand by differences in the coefficients of thermal expansion of thevarious components that are used to house the exterior mirror element.These components include a carrier plate used to attach the mirrorelement to the mechanism used to manipulate or adjust the position ofthe mirror (bonded to the mirror by an adhesive), a bezel and a housing.Many mirrors also typically have a potting material as a secondary seal.Each of these components, materials and adhesives have varyingcoefficients of thermal expansion that will expand and shrink to varyingdegrees during heating and cooling and will exert stress on the glasselements 112 and 114. On very large applications, including mirrors andwindows hydrostatic pressure becomes a concern and may lead to doubleimaging problems when the front and rear glass elements bow out at thebottom and bow in at the top of the mirror or window. By coupling thefront and rear glass elements the thin glass/free-standing gel/thinglass combination act as one thick unitary member (while still allowingproper operation of the electrochromic mirror or window) and therebyreduce or eliminate the bending, bowing, flexing, double image anddistortion problems and non-uniform coloring of the electrochromicmedium.

The cooperative interaction between the free-standing gel and the thinglass elements of the present invention also improves the safety aspectsof the electrochromic mirror 110 having thin glass elements. In additionto being more flexible, thin glass is more prone to breakage than thickglass. By coupling the free-standing gel with the thin glass the overallstrength is improved (as discussed above) and further restrictsshattering and scattering and eases clean-up in the case of breakage ofthe device.

The improved cross-linked polymer matrix used in the present inventionis disclosed in commonly assigned co-pending U.S. patent applicationSer. No. 08/616,967 entitled “IMPROVED ELECTROCHROMIC LAYER AND DEVICESCOMPRISING SAME” filed on Mar. 15, 1996, and the International PatentApplication filed on or about Mar. 15, 1997 and claiming priority tothis U.S. Patent Application. The entire disclosure of these twoApplications, including the references contained therein, are herebyincorporated herein by reference.

Generally, the polymer matrix results from crosslinking polymer chains,where the polymer chains are formed by the vinyl polymerization of amonomer having the general formula:

where R₁ is optional and may be selected from the group consisting of:alkyl, cycloalkyl, poly-cycloalkyl, heterocycloalkyl, carboxyl and alkyland alkenyl derivatives thereof; alkenyl, cycloalkenyl, cycloalkadienyl,poly-cycloalkadienyl, aryl and alkyl and alkenyl derivatives thereof,hydroxyalkyl; hydroxyalkenyl; alkoxyalkyl; and alkoxyalkenyl where eachof the compounds has from approximately 1 to approximately 20 carbonatoms. R₂ is optional and may be selected from the group consisting ofalkyl, cycloalkyl, alkoxyalkyl, carboxyl, phenyl and keto where each ofthe compounds has from approximately 1 to approximately 8 carbon atoms;and oxygen. R₃, R₄, and R₅ may be the same or different and may beselected from the group consisting of: hydrogen, alkyl, cycloalkyl,poly-cycloalkyl, heterocycloalkyl, and alkyl and alkenyl derivativesthereof; alkenyl, cycloalkenyl, cycloalkadienyl, poly-cycloalkadienyl,aryl and alkyl and alkenyl derivatives thereof; hydroxyalkyl;hydroxyalkenyl; alkoxyalkyl; alkoxyalkenyl; keto; acetoacetyl; vinylether and combinations thereof, where each of the compounds has fromapproximately 1 to approximately 8 carbon atoms. Finally, B may beselected from the group consisting of hydroxyl; cyanato; isocyanato;isothiocyanato; epoxide; silanes; ketenes; acetoacetyl, keto,carboxylate, imino, amine, aldehyde and vinyl ether. However, as will beunderstood by those skilled in the art, if B is an cyanato, isocyanato,isothiocyanato, or aldehyde it is generally preferred that R₁, R₂, R₃,R₄, and R₅ not have a hydroxyl functionality. Preferred among themonomers is methyl methacrylate; methyl acrylate; isocyanatoethylmethacrylate; 2-isocyanatoethyl acrylate; 2-hydroxyethyl methacrylate;2-hydroxyethyl acrylate; 3-hydroxypropyl methacrylate; glycidylmethacrylate; 4-vinylphenol; acetoacetoxy methacrylate and acetoacetoxyacrylate.

Electrochromic devices are sensitive to impurities, which is shownthrough poor cycle life, residual color of the electrochromic materialin its bleached state, and poor UV stability. Although many commercialprecursors are fairly pure and perform adequately as ordered,purification would improve their performance. They can not, however, bereadily purified by distillation because their low vapor pressure makeseven vacuum distillation difficult or impossible. On the other hand, themonomers used to make the polymer matrix can be purified and thus are asignificant advance in ensuring proper performance of an electrochromicdevice. This purification may be through chromatography, distillation,recrystalization or other purification techniques well known in the art.

The monomers of the preferred embodiment of the present invention shouldalso preferably be capable of pre-polymerization, typically in thesolvent utilized in the final electrochromic mirror. Bypre-polymerization we mean that the monomers and/or precursors reactwith one another to produce relatively long and relatively linearpolymers. These polymer chains will remain dissolved in the solvent andcan have molecular weights ranging from about 1,000 to about 300,000,although those skilled in the art will understand that molecular weightsof up to 3,000,000 are possible under certain conditions.

It should be understood that more than one monomer may bepre-polymerized together. Equation [I] shows the general formula for themonomers of the preferred embodiment of the present invention.Generally, any of the combinations of the monomers shown may be combinedinto one or more polymers (i.e., a polymer, a copolymer, terpolymer,etc.) in the pre-polymerization process. For example, one monomer may bepolymerized to give a homogeneous polymer material such as poly(2-hydroxyethyl methacrylate), poly (2-isocyanatoethyl methacrylate),and the like. However, it is generally preferred that a species with acrosslinking reactive component (e.g., hydroxyl, acetoacetyl,isocyanate, thiol etc.) be combined with another species either havingthe same crosslinking reactive component or no crosslinking reactivecomponent (e.g., methyl methacrylate, methyl acrylate, etc.). If acopolymer is produced, the ratio of the monomers without and with thecrosslinking components may range from about 200:1 to about 1:200. Anexample of these copolymers include hydroxyethyl methacrylate (HEMA)combined with methyl methacrylate (MMA) to form a copolymer. The ratioof HEMA to MMA may range form about 1:3 to about 1:50 with the preferredratio being about 1:10. The preferred crosslinker for any of thepre-polymers having a hydroxyl (or any reactive group having an activehydrogen, such as thiol, hydroxyl, acetoacetyl, urea, melamine,urethane, etc.) is an isocyanate, isothiocyanate, and the like having afunctionality greater than one. Also, 2-isocyanatoethyl methacrylate(IEMA) may be combined with MMA in the ratio of about 1:3 to about 1:50with the preferred ratio of about 1:10. Crosslinking of any of thepolymer chains containing an isocyanate can occur with any di- orpoly-functional compound containing a reactive hydrogen, such ashydroxyl, thiol, acetoacetyl, urea, melamine, urethanes, with hydroxylbeing presently preferred. These must have a functionality greater thanone and may be the same as those described hereinabove, aliphatic oraromatic compounds or, preferably, may be 4,4′-isopropylidenediphenol,4-4′(1-4 phenylenediisopropylidene) bisphenol, 4-4′(1-3phenylenediisopropylidene), or bisphenol 1,3-dihydroxy benzene. Althoughthe above description relates to copolymers, it will be understood bythose skilled in the art that more complex structures (terpolymers,etc.) may be made using the same teachings.

Finally, two copolymers may be combined such that they crosslink withone another. For example HEMA/MMA may be combined with IEMA/MMA and thehydroxyl groups of HEMA will self-react with the isocyanate groups ofIEMA to form an open polymeric structure. It should be understood thatthe rates of crosslinking for any of the polymers described herein canbe controlled by proper selection of the reactive crosslinking speciesemployed. For example, reaction rates can be increased by using anaromatic isocyanate or an aromatic alcohol or both. Reaction rates canbe decreased, for example, by using sterically hindered isocyanates orsterically hindered alcohols or both.

It should also be noted that the rigidity of the free standing gel canbe altered by changing the polymer molecular weight, the weight percentof the polymer and the crosslink density of the polymer matrix. The gelrigidity generally increases with increasing polymer concentration(weight percent), increasing crosslink density and to some extent withincreasing molecular weight.

During operation, light rays enter through the front glass 112, thetransparent conductive layer(s) 118, the free-standing gel and at leastone electrochromic material in chamber 116, the transparent conductivelayer 120 and the back glass 114, before being reflected from thereflector 124 provided on the fourth surface 114 b of the mirror 110.Light in the reflected rays exit by the same general path traversed inthe reverse direction. Both the entering rays and the reflected rays areattenuated in proportion to the degree to which the gelledelectrochromic medium 124 is light absorbing. Alternatively, as statedabove, the reflector may be placed on the third surface 114 a inaccordance with the disclosure of U.S. patent application entitled“ELECTROCHROMIC REARVIEW MIRROR INCORPORATING A THIRD SURFACE METALREFLECTOR” filed on or about Apr. 2, 1997. The entire disclosure of thisU.S. patent application is hereby incorporated herein by reference. Inthis case the third surface reflector doubles as an electrode and thetransparent conductive layer 120 may optionally be deleted. Further, ifthe reflector is placed on the third surface 114 a, a heater 138 may beplaced on the fourth surface 114 b in accordance with the teachings inthe immediately above-referenced U.S. patent application.

The at least one electrochromic material may be a wide variety ofmaterials capable of changing properties such that light travelingtherethrough is attenuated but must be capable of being dissolved in thesolvent. In order to balance charge during the electrochromic reactions,another redox active material must be present. This other material mayinclude solution-phase redox, solid-state, and metal or viologen saltdeposition; however, solution phase redox is presently preferred, suchas those disclosed in above-referenced U.S. Pat. Nos. 4,902,108;5,128,799, 5,278,693; 5,280,380; 5,282,077; 5,294,376; 5,336,448.

One or more layers of a transparent electrically conductive material 118are deposited on the second surface 112 b to act as an electrode.Transparent conductive material 118 may be any material which: bondswell to front element 112 and maintains this bond when the epoxy seal122 bonds thereto; is resistant to corrosion with any materials withinthe electrochromic device; is resistant to corrosion by the atmosphere;and has minimal diffuse or specular reflectance, high lighttransmission, neutral coloration and good electrical conductance.Transparent conductive material 118 may be fluorine doped tin oxide,indium doped tin oxide (ITO), ITO/metal/ITO (IMI) as disclosed in“Transparent Conductive Multilayer-Systems for FPD Applications”, by J.Stollenwerk, B. Ocker, K. H. Kretschmer of LEYBOLD AG, Alzenau, Germany,and the materials described in above-referenced U.S. Pat. No. 5,202,787,such as TEC 20 or TEC 15, available from Libbey Owens-Ford Co. (LOF) ofToledo, Ohio. Similar requirements are needed for whatever is depositedonto the third surface 114 a, whether it is another layer of transparentconductive material 120 (in the case of a window) or a combinedreflector/electrode (in the case of a mirror).

The conductance of transparent conductive material 118 will depend onits thickness and composition, but as a general rule atmosphericpressure chemical vapor deposition (APCVD) applied coatings, such as TECcoatings from LOF, are cheaper than vacuum-deposited coatings, such asITO coatings, and more importantly they are more color-neutral. Thiscolor neutrality of the coatings is especially pronounced when themirrors are in their full colored or darkened state because in this darkstate the primary sources of the reflection viewed by a vehicle occupantare the reflections from the first and second surface of the device.Thus, the transparent coating 118 disposed on the second surface 112 bhas a greater influence on the color neutrality of the device when thedevice is in a highly or full darkened state. Another factor to beconsidered is that, although both ITO and the TEC coatings will work astransparent conductors in mirrors having thick glass elements, the TECcoatings cannot to date be applied onto glass having a thickness lessthan about 2 mm while the glass is on the production float-line used tomanufacture sheets of glass. Thus, TEC coatings are not presentlyavailable on thin glass. This leads to color matching problems becausethere are cases where it is beneficial to have an interior mirror withlow cost thick glass elements and an exterior mirror with light weightthin glass elements and have both mirrors on the same vehicle. Theinside mirror (110 in FIG. 1) having thick glass can use the inexpensiveTEC coatings on the second surface and therefore, when the mirror is inthe darkened state, the reflected image is color-neutral. However, theoutside mirrors (111 a and/or 111 b of FIG. 1) having thin glass mustuse the expensive ITO coatings on the second surface and therefore, whenthe mirror is in the darkened state, the reflected image is notcompletely color-neutral—and therefore not color-matched with the insidemirror.

In addition, TEC coatings can cause difficulties when applied to glassthat must then be bent or curved to a convex or aspheric shape,irrespective of the thickness of the glass, because each glass elementmust have a substantially similar radius of curvature. The TEC coatingsare applied during the manufacture of the glass to the side of the glassthat is not in contact with the tin bath or the rollers (i.e., thedeposition is on the “clean” side of the glass). Since the glass bendingprocess occurs after the glass is produced, the TEC coatings are presenton the glass surface when the glass is bent. During the bending processthe glass element is heated to high temperatures, and although notknowing the exact mechanism, it is believed that the difference in thecoefficient of thermal expansion between the glass and the conductivecoating, and/or the difference in emissivity between the coated anduncoated sides of the glass, tend to alter the flexing properties of thecombined glass/coating structure during cooling. If a mirror with afourth surface reflector is produced, then the TEC coatings will beplaced on the second (concave) and third (convex) surfaces, and becauseof the altered flexing properties, each glass element will have adifferent radius of curvature. If a mirror with a third surfacereflector is produced, two problems occur. First, to get similar radiiof curvature, a TEC coating must be placed on the second and fourthsurfaces, but the fourth surface TEC coating is essentially useless anddoes nothing but increase the unit price of the mirror. Second, thereflector/electrode that is applied to the third surface has to beapplied to the “dirty” side of the glass that was in contact with thetin bath and the rollers. This leads to problems well known in the artsuch as tin bloom, sulfur stain and roller marks, all of which causeadverse side effects in electrochromic mirrors. ITO coatings can beapplied to the second surface after the glass is bent to alleviate theseproblems, however, this leads to the same color-neutrality andcolor-matching problems outlined above.

In accordance with another aspect of the present invention, a multilayercolor-neutral transparent conductive coating 118 can be used on thesecond surface of an exterior mirror (111 a and/or 111 b of FIG. 1)having thin or bent glass, in combination with an interior mirror havingTEC coatings on the second surface such that the mirror-system iscolor-neutral and color-matched. This color-neutral transparentconductive coating includes a thin (e.g., between about 150 angstromsand about 500 angstroms) first transparent layer 118 a having a highrefractive index, followed by thin (e.g., between about 150 angstromsand about 500 angstroms) second transparent layer 118 b having a lowrefractive index, followed by a thick (e.g., between about 800 angstromsand about 3500 angstroms) third conductive transparent layer 118 chaving a high refractive index. Glass has a refractive index of about1.5; the first two thin layers generally having refractive indices ofabout 2.0 and about 1.5, respectively, tend to act in concert to formone layer having a medium refractive index of about 1.75. The thick topcoating has a refractive index of about 2.0. Thus a stack is producedhaving refractive indices of approximately 1.5/1.75/2.0. The presentlypreferred compositions and thicknesses for each layer of the multi-layerstack are: about 200-400 angstroms of ITO for the first layer 118 a;about 200-400 angstroms of SiO₂ for the second layer 118 b and about1500 angstroms of ITO for the third layer 118 c. This gradation betweenlow and high refractive indices produces a transparent conductivecoating that is color-neutral, which matches the color-neutral TECcoatings on the second surface of the inside mirror—leaving aninside/outside color-matched mirror system.

In accordance with yet another embodiment of the present invention, anadditional advantage of thin glass construction is improved opticalimage quality for convex, aspheric and all electrochromic devices,including mirrors and windows that are not flat. It is difficult toreproducibly bend glass and obtain identical local and global radii ofcurvature for each pair of glass elements. However, most electrochromicmirrors are made by bonding two glass elements together in a nominallyparallel, planar, spaced-apart relationship and any deviation fromparallelism manifests itself as distortion, double image and non-uniformspacing between the two glass elements. The double image phenomena isdue to mismatch in the curvature of the glass elements which results inmisalignment between the residual and secondary reflections from thefront glass element and its transparent conducting coating and thereflections from the main reflector layer. This is extensively discussedin above-referenced U.S. patent application entitled “ELECTROCHROMICREARVIEW MIRROR INCORPORATING A THIRD SURFACE METAL REFLECTOR”. Changingthe reflector layer from the fourth surface to the third surface helpsreduce double imaging because the distance between the first surface,residual reflectance, and the reflectance form the main reflector isreduced. This is especially beneficial for mirrors using bent glass.Combining the use of a third surface reflector layer with the use of athin glass front element provides a remarkable advantage for mirrorsusing bent glass since the residual and the main reflections are soclose there is little or no double image. This is the case even when theglass is bent in normal bending processes that give rise to significantvariations in the local and overall radius of curvature between the twoglass elements used to make the mirror. The combination of a thirdsurface reflector/electrode and thin glass front element provides amirror that nearly equals the optical image quality of a true firstsurface reflector mirror even when the glass is bent.

The coating 120 of the third surface 114 a is sealably bonded to thecoating 118 on the second surface 112 b near their outer perimeters by asealing member 122. Preferably, sealing member 122 contains glass beads(not shown) to hold transparent elements 112 and 114 in a parallel andspaced apart relationship while the seal material cures. Sealing member122 may be any material which is capable of adhesively bonding thecoatings on the second surface 112 b to the coatings on the thirdsurface 114 a to seal the perimeter such that electrochromic material124 does not leak from chamber 116 while simultaneously maintaining agenerally constant distance therebetween. Optionally, the layer oftransparent conductive coating 118 and the layer on the third surface120 (transparent conductive material or reflector/electrode) may beremoved over a portion where sealing member is disposed (not the entireportion, otherwise the drive potential could not be applied to the twocoatings). In such a case, sealing member 118 must bond well to glass.

The performance requirements for a perimeter seal member 122 used in anelectrochromic device are similar to those for a perimeter seal used ina liquid crystal device (LCD) which are well known in the art. The sealmust have good adhesion to glass, metals and metal oxides, must have lowpermeabilities for oxygen, moisture vapor and other detrimental vaporsand gases, and must not interact with or poison the electrochromic orliquid crystal material it is meant to contain and protect. Theperimeter seal can be applied by means commonly used in the LCD industrysuch as by silk-screening or dispensing. Totally hermetic seals such asthose made with glass frit or solder glass can be used, but the hightemperatures involved in processing (usually near 450-degreesCentigrade) this type of seal can cause numerous problems such as glasssubstrate warpage, changes in the properties of transparent conductiveelectrode and oxidation or degradation of the reflector. Because oftheir lower processing temperatures, thermoplastic, thermosetting or UVcuring organic sealing resins are preferred. Such organic resin sealingsystems for LCD's are described in U.S. Pat. Nos. 4,297,401, 4,418,102,4,695,490, 5,596,023 and 5,596,024. Because of their excellent adhesionto glass, low oxygen permeability and good solvent resistance, epoxybased organic sealing resins are preferred. These epoxy resin seals maybe UV curing, such as described in U.S. Pat. No. 4,297,401, or thermallycuring, such as with mixtures of liquid epoxy resin with liquidpolyamide resin or dicyandiamide, or they can be homopolymerized. Theepoxy resin may contain fillers or thickeners to reduce flow andshrinkage such as fumed silica, silica, mica, clay, calcium carbonate,alumina, etc., and/or pigments to add color. Fillers pretreated withhydrophobic or silane surface treatments are preferred. Cured resincrosslink density can be controlled by use of mixtures ofmono-functional, di-functional and multi-functional epoxy resins andcuring agents. Additives such as silanes or titanates can be used toimprove the seal's hydrolytic stability, and spacers such as glass beadsor rods can be used to control final seal thickness and substratespacing. Suitable epoxy resins for use in a perimeter seal member 122include but are not limited to: “EPON RESIN” 813, 825, 826, 828, 830,834, 862, 1001F, 1002F, 2012, DPS-155, 164, 1031, 1074, 58005, 58006,58034, 58901, 871, 872 and DPL-862 available from Shell Chemical Co.,Houston, Tex.; “ARALITE” GY 6010, GY 6020, CY 9579, GT 7071, XU 248, EPN1139, EPN 1138, PY 307, ECN 1235, ECN 1273, ECN 1280, MT 0163, MY 720,MY 0500, MY 0510 and PT 810 available from Ciba Geigy, Hawthorne, N.Y.;“D.E.R.” 331, 317, 361, 383, 661, 662, 667, 732, 736, “D.E.N.” 431, 438,439 and 444 available from Dow Chemical Co., Midland, Mich. Suitableepoxy curing agents include V-15, V-25 and V-40 polyamides from ShellChemical Co.; “AJICURE” PN-23, PN-34 and VDH available from AjinomotoCo., Tokyo, Japan; “CUREZOL” AMZ, 2MZ, 2E4MZ, C11Z, C17Z, 2PZ, 21Z and2P4MZ available from Shikoku Fine Chemicals, Tokyo, Japan; “ERISYS” DDAor DDA accelerated with U-405, 24EMI, U-410 and U-415 available from CVCSpecialty Chemicals, Maple Shade, N.J..; “AMICURE” PACM, 352, CG, CG-325and CG-1200 available from Air Products, Allentown, Pa. Suitable fillersinclude fumed silica such as “CAB-O-SIL” L-90, LM-130, LM-5, PTG, M-5,MS-7, MS-55, TS-720, HS-5, EH-5 available from Cabot Corporation,Tuscola, Ill.; “AEROSIL” R972, R974, R805, R812, R812 S, R202, US204 andUS206 available from Degussa, Akron, Ohio. Suitable clay fillers includeBUCA, CATALPO, ASP NC, SATINTONE 5, SATINTONE SP-33, TRANSLINK 37,TRANSLINK 77, TRANSLINK 445, TRANSLINK 555 available from EngelhardCorporation, Edison, N.J. Suitable silica fillers are SILCRON G-130,G-300, G-100-T and G-100 available from SCM Chemicals, Baltimore, Md.Suitable silane coupling agents to improve the seal's hydrolyticstability are Z-6020, Z-6030, Z-6032, Z-6040, Z-6075 and Z-6076available from Dow Corning Corporation, Midland, Mich. Suitableprecision glass microbead spacers are available in an assortment ofsizes from Duke Scientific, Palo Alto, Calif.

In the assembly and manufacture of electrochromic devices polymericbeads may be applied to the electrochromic mirror area on the viewingarea of the second or third surface, i.e., inboard of the perimeterseal, to temporarily maintain proper cell spacing during themanufacturing process. These beads are even more useful with deviceshaving thin glass elements because they help prevent distortion anddouble image during device manufacture and maintain a uniformelectrochromic medium thickness until gellation occurs. It is desirablethat these beads comprise a material that will dissolve in theelectrochromic medium and is benign to the electrochromic system whilebeing compatible with whatever electrochromic system is contained withinthe chamber 116 (e.g., the constituents of gelled layer 124). While theuse of PMMA beads is known, they are not preferred because they have thefollowing disadvantages: they require a heat cycle (generally at least 2hours at 85 degrees C.) to dissolve, they do not dissolve before thepreferred gels of the present invention crosslink, they can cause lightrefracting imperfections in gelled and non-gelled electrochromicdevices, and they can cause the electrochromic medium to color and clearmore slowly near the area where beads were prior to dissolving.

In accordance with another aspect of the present invention, polymericbeads 117, that dissolve within an electrochromic device at ambient ornear-ambient temperatures without imparting refractive imperfections,are placed or sprinkled on the second or third surface within theviewing area of the mirror or a window so that they prevent distortionand maintain cell spacing during manufacturing and dissolve very soonthereafter.

The polymeric beads 117 can be incorporated into an electrochromicmirror as follows: The perimeter sealing resin is charged with glassbeads of the appropriate size desired for the final cell gap (typicallyaround 135 microns in diameter for a solution-phase insideelectrochromic mirror) at a level of about ½ weight percent. Drypolymeric beads 117 that are sized about 10% larger than the glass beadsare loaded into a “salt shaker” type container with holes on one end.The rear glass element 114 is laid flat with the inside electrodesurface (third surface) facing up. Plastic beads are sprinkled onto thecoating (120) disposed on the third surface 114 a using the salt shakerto a concentration of about 5 to 10 beads per square centimeter. Theperimeter sealing member 122 is applied around the edges of the surfaceof the transparent conductive electrode on the rear surface of the frontelement 112 by dispensing or silk screening as is typical for themanufacture of LCD's, such that seal material covers the entireperimeter except for a gap of about 2 mm along one edge. This gap in theseal will be used as a fill port (not shown) to introduce theelectrochromic medium after assembly of the glass plates and curing ofthe seal. After seal application, the glass plates are assembledtogether by laying the first glass plate on top of the second glassplate and the assembly is pressed until the gap between the glass platesis determined by the glass and plastic spacers. The sealing member 122is then cured. The electrochromic cell is then placed fill port down inan empty container or trough in a vacuum vessel and evacuated.Electrochromic fluid media is introduced into the trough or containersuch that the fill port is submerged. The vacuum vessel is thenbackfilled which forces the fluid electrochromic material through thefill port and into the chamber 116. The fill port is then plugged withan adhesive, typically a UV light curing adhesive, and the plug materialis cured. This vacuum filling and plugging process is commonly used inthe LCD industry. If the proper polymeric bead material 117 is used, thebeads will dissolve in the electrochromic medium without leaving a traceat room temperature or by applying moderate heat as the electrochromicmedium gels thereby permanently fixing the cell gap.

Generally, these polymeric beads comprise a material that will readilydissolve in organic solvents, such as, for example, propylene carbonate,at ambient or near-ambient temperatures. The materials should dissolvein the electrochromic medium either within the time it takes thefree-standing gel to crosslink (which generally takes around 24 hours),but not so fast that they do not provide a spacer function duringprocessing (e.g., sealing and vacuum backfilling) of the mirror element.Materials that meet the above requirements include the followingcopolymers available from ICI Acrylics, Wilmington, Del.: “ELVACITE”2008, a MMA/methacrylic acid copolymer, “ELVACITE” 2010, aMMA/ethylacrylate copolymer, “ELVACITE” 2013, and a MMA/n-butylacrylatecopolymer, as well as poly(propylene carbonate), with “ELVACITE” 2013being presently preferred. In addition to these copolymers, it isbelieved that materials such as various polyacrylates and polyethers maybe suitable for the dissolvable beads.

Since the beads are used to maintain cell spacing for a short timeduring manufacture, they should preferably have a diameter equal to orslightly larger than the cell spacing of the device, which can beaccomplished by sieving through successive screens to obtain the desiredsize. Sieves of the appropriate size can be purchased from ATM,Milwaukee, Wis. If 135 micron glass beads will be loaded into thesealing resin, the preferred plastic bead size would be about 10% largeror 148 microns. To sieve plastic beads to the 148 micron range, astandard 145 micron and a standard 150 micron sieve would be required.If a tighter range is desired, custom-sized sieves could be ordered foran additional cost. The 150 micron sieve is placed on top of the 145micron sieve and the top 150 micron sieve is charged with unsizedplastic beads. The sieves are then vibrated such that beads smaller than150 microns will fall through the holes in the 150 micron sieve. Beadssmaller than 145 microns will fall through the bottom 145 micron sieve,and beads between 145 and 150 microns in size will be captured betweenthe 145 micron and the 150 micron sieves. If the beads tend to clump orstick together, effective separation can be achieved by flushing aliquid such as water through the sieve stack while vibrating the sieves.Beads wet-sieved in this manner must be thoroughly dried before use suchas by oven baking at 80° C. for 2 hours.

Electrochromic devices having a thin glass element/gelled electrochromicmedium/thin glass element configuration as provided herein can be usedin a wide variety of applications wherein the transmitted or reflectedlight can be modulated. Such devices include rearview mirrors forvehicles; windows for the exterior of a building, home or vehicle;skylights for buildings including tubular light filters; windows inoffice or room partitions; display devices; contrast enhancement filtersfor displays; light filters for photographic devices and light sensors;and indicators for power cells as well as primary and secondaryelectrochemical cells.

It will be understood that the term “glass” may be referred to herein asglass, coated glass, layered glass, and/or glass doped with, forexample, metals, metal oxides, dyes, additives, and/or other compoundsor materials used to affect the transmission properties of a glasselement.

The present invention is also directed to an electrochromic device whichcomprises: (1) a first glass element having an electrically conductivematerial associated therewith, wherein the first element comprises aheight (h₁) , a width (w₂) , a thickness (t₁), an inner surface, and anouter surface; (2) a second glass element having an electricallyconductive material associated therewith, wherein the second elementcomprises a height (h₂) , a width (w₂) , and a thickness (t₂), an innersurface, and an outer surface; (3) a cell spacing (c) which comprises adistance between the inner surface of the first element and the innersurface of the second element; (4) a gelled electrochromic mediumcontained within a chamber positioned between the first and secondelements; (5) wherein (h₁), (w₁), (t₁), (h₂), (w₂), (t₂), and (c) arenumerical values in millimeters; and (6) wherein (h₁), (w₁), and (t₁) ofthe first element, and (h₂), (w₂), and (t₂) of the second element and(c) comprise numerical values such that the following inequality issatisfied:${\frac{2{h_{1}^{5}\left( {1 - ^{- 2^{{({h_{1}/w_{1}})}^{2}}}} \right)}}{t_{1}^{3}\left( {7.57 \times 10^{12}} \right)} + \frac{2{h_{2}^{5}\left( {1 - ^{- 2^{{({h_{2}/w_{2}})}^{2}}}} \right)}}{t_{2}^{3}\left( {7.57 \times 10^{12}} \right)}} \geq {{.1}{(c).}}$

In accordance with the present invention, it has been experimentallydetermined that when (h₁), (w₁), and (t₁) of the first element and (h₂),(w₂), and (t₂) of the second element generate a value for the left sideof the above-identified inequality that is greater than approximately10% of the cell spacing (c), then a gelled electrochromic medium isnecessary to substantially preclude, among other things, undesirableoptical distortion associated with the electrochromic device. Indeed, ifthe above-identified inequality is satisfied, then displacement orwarping of at least one of the two elements facilitates opticaldistortion. Such displacement or warping can become readily problematicfor electrochromic devices which are larger and/or thinner than, forexample, conventional rearview mirrors, such as large scaleelectrochromic exterior mirrors for trucks and other motor vehicles, aswell as for electrochromic window applications—just to name a few.

The above-identified inequality was obtained by conducting finiteelemental analysis on glass elements to evaluate their degree ofdisplacement while under hydrostatic load. The displacement of eachelement was then correlated as a function its height, width, andthickness. With the upper threshold limit for allowable,non-objectionable element displacement being approximately 10% of thecell spacing for an associated electrochromic device, the followingelements were examined to determine whether or not a gelledelectrochromic medium was required in the associated electrochromicdevice:

TABLE I Element Gelled Height: Cell Electrochromic Width:ThicknessSpacing Inequality Medium Experiment (mm) (mm) Satisfied Required A 55:250:2.2 0.137 No No B 390:135:2.2 0.200 Yes Yes C 150:245:1.6 0.180No No-Approx- imate Threshold

As can be seen from Table I, an electrochromic device which incorporateselements from experiment A does not require a gelled electrochromicmedium. However, if an electrochromic device incorporates elements fromexperiment B, then a gelled electrochromic medium is clearly required.Experiment C provides one example of an upper threshold limit where agelled electrochromic medium is not required.

The following additional illustrative examples are not intended to limitthe scope of this invention but to illustrate its application and use:

EXAMPLE 1

Several electrochromic devices containing a free-standing gel wereprepared as follows. A solution of 1.5114 grams ofbis(1,1′-3-phenylpropyl)-4,4′-dipyridinium bis(tetrafluoroborate) in37.02 grams of a copolymer of 1:10 isocyanate ethyl methacrylate/methylmethacrylate was mixed with a solution comprising 0.7396 grams ofBisphenol A, 0.4606 grams of 5,10-dimethyl-5,10-dihydrophenazine, 0.5218grams of Tinuvin P (Ciba Geigy, Tarrytown, N.Y.) in 57.36 grams ofpropylene carbonate. This mixture was vacuum backfilled into severalindividual devices having two 1.1 mm glass elements that were sealedtogether with an epoxy seal, with a 180 micron cell spacing, thatcontained polymeric spacer beads comprising poly(propylene carbonate),available from Sigma-Aldrich, “ELVACITE” 2008, 2010, 2013, and 2041,respectively. The gel formation was carried out at ambient temperatures(20-25 degrees Celsius). The devices were approximately 4″×6″ and weresubjected to a vibration test consisting of a five hundred G-appliedshock load with a 6 point random axis of rotation, with temperaturescycling repetitively from −100 degrees Celsius to 100 degrees Celsiusover a four minute ramp for a total of 25 cycles. These devices allshowed excellent vibrational resistance. Additionally, all of the spacerbeads dissolved within 24 hours from when the devices were filled withthe gel mixture.

EXAMPLE 2

Several electrochromic devices were prepared in accordance with Example1, except the size of the device elements were approximately 5″×9″. Allof the spacer beads dissolved within 24 hours from when the devices werefilled with the gel mixture. These devices were subjected to a pressurepoint resistance test. These parts, having significant area, haveinherent points at which they are more susceptible to breakage underexternally applied pressure. One of these points (approximately 0.5inches form the edge) was selected for testing. These parts showed nobreakage even at 1235 pounds, which represents the maximum attainablepressure on the testing equipment used (a Chattilon Force MeasurementGauge ET-110, with a rounded hard plastic finger of 1″ diameter). Uponreleasing the 1235 pounds of pressure, it was noted that, due to theextreme pressure, the gel had been forced out from an area approximately0.5 inches in diameter immediately under the plastic test finger. Theglass elements appeared to have contacted one another as well. Withinmoments after removing the external pressure, the gel “self-healed” andresumed its original position at the test point. For comparison, partscontaining no free-standing gel and having glass elements withthicknesses of about 1.1 mm and PMMA beads showed glass breakage at anaverage of 167 pounds.

While the invention has been described in detail herein in accordancewith certain preferred embodiments thereof, many modifications andchanges therein may be effected by those skilled in the art withoutdeparting from the spirit of the invention. Accordingly, it is ourintent to be limited only by the scope of the appending claims and notby way of the details and instrumentalities describing the embodimentsshown herein.

What is claimed is:
 1. An electrochromic device, comprising: a firstglass element having an electrically conductive material associatedtherewith, wherein said first element comprises a height (h₁) , a width(w₁) , a thickness (t₁), an inner surface, and an outer surface; asecond glass element having an electrically conductive materialassociated therewith, wherein said second element comprises a height(h₂) , a width (w₂), and a thickness (t₂), an inner surface, and anouter surface; a cell spacing (c) which comprises a distance betweensaid inner surface of said first element and said inner surface of saidsecond element; a gelled electrochromic medium contained within achamber positioned between said first and second elements; wherein (h₁),(w₁), (t₁), (h₂), (w₂), (t₂), and (c) are numerical values inmillimeters, wherein (t₁) and (t₂) having thickness of at least 0.5 mm;and wherein (h₁), (w₁), and (t₁) of said first element, and (h₂), (w₂),and (t₂) of said second element and (c) comprise numerical values suchthat the following inequality is satisfied:${\frac{2{h_{1}^{5}\left( {1 - ^{- 2^{{({h_{1}/w_{1}})}^{2}}}} \right)}}{t_{1}^{3}\left( {7.57 \times 10^{12}} \right)} + \frac{2{h_{2}^{5}\left( {1 - ^{- 2^{{({h_{2}/w_{2}})}^{2}}}} \right)}}{t_{2}^{3}\left( {7.57 \times 10^{12}} \right)}} \geq {{.1}{(c).}}$


2. The electrochromic device according to claim 1, wherein said firstand second elements are substantially linear.
 3. The electrochromicdevice according to claim 1, wherein said first and second elements arebent to a convex shape.
 4. The electrochromic device according to claim1, wherein said first and second elements are bent to an aspheric shape.5. The electrochromic device according to claim 1, wherein said gelledelectrochromic medium comprises a crosslinked polymer matrix.
 6. Anelectrochromic device, comprising: a first glass element having anelectrically conductive material associated therewith, wherein saidfirst element comprises a height (h₁), a width (w₁), a thickness (t₁),an inner surface, and an outer surface; a second glass element having anelectrically conductive material associated therewith, wherein saidsecond element comprises a height (h₂) , a width (w₂) , and a thickness(t₂), an inner surface, and an outer surface; a cell spacing (c) whichcomprises a distance between said inner surface of said first elementand said inner surface of said second element; a gelled electrochromicmedium contained within a chamber positioned between said first andsecond elements; wherein (h₁), (w₁), (t₁), (h₂), (w₂), (t₂), and (c) areindependent numerical values in millimeters, wherein (t₁) and (t₂)having thickness of at least 0.5 mm; and wherein (h₁), (w₁), and (t₁) ofsaid first element, and (h₂), (w₂), and (t₂) of said second element and(c) comprise numerical values such that the following inequality issatisfied:${\frac{2{h_{1}^{5}\left( {1 - ^{- 2^{{({h_{1}/w_{1}})}^{2}}}} \right)}}{t_{1}^{3}\left( {7.57 \times 10^{12}} \right)} + \frac{2{h_{2}^{5}\left( {1 - ^{- 2^{{({h_{2}/w_{2}})}^{2}}}} \right)}}{t_{2}^{3}\left( {7.57 \times 10^{12}} \right)}} \approx {0.1{(c).}}$


7. The electrochromic device according to claim 6, wherein said firstand second elements are substantially linear.
 8. The electrochromicdevice according to claim 6, wherein said first and second elements arebent to a convex shape.
 9. The electrochromic device according to claim6, wherein said first and second elements are bent to an aspheric shape.10. The electrochromic device according to claim 6, wherein said gelledelectrochromic medium comprises a crosslinked polymer matrix.
 11. Anelectrochromic device, comprising: thin front and rear spaced glasselements, each having front and rear surfaces, wherein said frontelement comprises a height (h₁), a width (w₁), a thickness (t₁) and saidrear element comprises a height (h₂), a width (w₂), and a thickness(t₂); a layer of transparent conductive material disposed on said rearsurface of said front element and on said front surface of said rearelement; a reflector disposed on one side of said rear element providedthat, if said reflector is on said rear surface of said rear element,then said front surface of said rear element contains a layer of atransparent conductive material; a perimeter sealing member bondingtogether said front and rear spaced elements in a spaced-apartrelationship to define a chamber therebetween, where said chambercontains a free-standing gel comprising a solvent and a crosslinkedpolymer matrix, and wherein said chamber further contains at least oneelectrochromic material in solution with said solvent and, as part ofsaid solution, interspersed in said crosslinked polymer matrix; whereinsaid polymer matrix cooperatively interacts with said front and rearelements to form one thick, strong unitary member, and where saidreflector is effective to reflect light through said chamber and saidfront element when said light reaches said reflector after passingthrough said front element and said chamber; a cell spacing (c) whichcomprises a distance between said rear surface of said front element andsaid front surface of said rear element; wherein (h₁), (w₁), (t₁), (h₂),(w₂), (t₂), and (c) are numerical values in millimeters, wherein (t₁)and (t₂) having thickness of at least 0.5 mm; and wherein (h₁), (w₁),and (t₁) of said first element, and (h₂), (w₂), and (t₂) of said secondelement and (c) comprise numerical values such that the followinginequality is satisfied:${\frac{2{h_{1}^{5}\left( {1 - ^{- 2^{{({h_{1}/w_{1}})}^{2}}}} \right)}}{t_{1}^{3}\left( {7.57 \times 10^{12}} \right)} + \frac{2{h_{2}^{5}\left( {1 - ^{- 2^{{({h_{2}/w_{2}})}^{2}}}} \right)}}{t_{2}^{3}\left( {7.57 \times 10^{12}} \right)}} \geq {0.1{(c).}}$


12. The electrochromic device according to claim 11, wherein said firstand second elements are substantially linear.
 13. The electrochromicdevice according to claim 11, wherein said first and second elements arebent to a convex shape.
 14. The electrochromic device according to claim11, wherein said first and second elements are bent to an asphericshape.
 15. The electrochromic device according to claim 11, wherein saidpolymer matrix results from crosslinking polymer chains and where saidpolymer chains are formed by polymerizing at least one monomer selectedfrom the group consisting of: methyl methacrylate; methyl acrylate;2-isocyanatoethyl methacrylate; 2-isocyanatoethyl acrylate;2-hydroxyethyl methacrylate; 2-hydroxyethyl acrylate; 3-hydroxypropylmethacrylate; vinyl ether n-butyl methyl methacrylate; tetraethyleneglycol vinyl ether; glycidyl methacrylate; 4-vinylphenol;acetoacetoxyethyl methacrylate and acetoacetoxyethyl acrylate.
 16. Theelectrochromic device according to claim 15, wherein said polymer chainsare cross-linked by reaction with a compound having a functional groupselected from the group consisting of aromatic and aliphatic hydroxyl;aromatic and aliphatic cyanato; aromatic and aliphatic isocyanato;aliphatic and aromatic isothiocyanato, with a functionality of at least2.
 17. The electrochromic device according to claim 15, wherein saidpolymer chains results from the polymerization of at least two distinctmonomers.
 18. The electrochromic device according to claim 15, whereinsaid at least two monomers are selected from the group consisting of:methyl methacrylate; methyl acrylate; 2-isocyanatoethyl methacrylate;2-isocyanatoethyl acrylate; 2-hydroxyethyl methacrylate; 2-hydroxyethylacrylate; 3-hydroxypropyl methacrylate; vinyl ether n-butyl methylmethacrylate; tetraethylene glycol divinyl ether; glycidyl methacrylate;4-vinylphenol; acetoacetoxyethyl methacrylate and acetoacetoxyethylacrylate.
 19. The electrochromic device according to claim 18, whereinsaid at least two monomers are selected from the group consisting of:methyl methacrylate; 2-isocyanatoethyl methacrylate; 2-hydroxyethylmethacrylate; and glycidyl methacrylate.
 20. The electrochromic deviceaccording to claim 19, wherein said at least two monomers comprise2-hydroxyethyl methacrylate and methyl methacrylate.
 21. Theelectrochromic device according to claim 20, wherein the ratio of2-hydroxyethyl methacrylate to methyl methacrylate is about 1:10. 22.The electrochromic device according to claim 20, wherein said polymerchains formed from at least 2-hydroxyethyl methacrylate and methylmethacrylate are crosslinked by a compound having more than onefunctional group that will react with an active hydrogen.
 23. Theelectrochromic device according to claim 19, wherein said at least twomonomers comprise isocyanatoethyl methacrylate and methyl methacrylate.24. The electrochromic device according to claim 23, wherein the ratioof isocyanatoethyl methacrylate to methyl methacrylate ranges from about1:3 to about 1:50.
 25. The electrochromic device according to claim 24,wherein the ratio of isocyanatoethyl methacrylate to methyl methacrylateis about 1:20.
 26. The electrochromic device according to claim 24,wherein said polymer chains formed from at least isocyanatoethylmethacrylate and methyl methacrylate are crosslinked by a compoundhaving a functional group containing more than one active hydrogen. 27.The electrochromic device according to claim 15, wherein said polymermatrix is formed from at least two distinct polymer chains, each of saidat least two distinct polymer chains comprise at least one monomerselected from the group consisting of methyl methacrylate and methylacrylate polymerized with at least one monomer selected from the groupconsisting of 2-isocyanatoethyl methacrylate; 2-isocyanatoethylacrylate; 2-hydroxyethyl methacrylate; 2-hydroxyethyl acrylate;3-hydroxypropyl methacrylate; glycidyl methacrylate; 4-vinylphenol;acetoacetoxyethyl methacrylate; vinyl ether n-butyl methyl methacrylateand acetoacetoxyethyl acrylate, where said first and second polymerchains may be the same or different.
 28. The electrochromic deviceaccording to claim 27, wherein said first of said at least two polymerchains comprises a copolymer of isocyanatoethyl methacrylate and methylmethacrylate and where said second of said at least two polymer chainscomprises a copolymer of 2-hydroxyethyl methacrylate and methylmethacrylate.
 29. The electrochromic device according to claim 28,wherein where the ratio of isocyanatoethyl methacrylate and methylmethacrylate ranges from about 1:3 to about 1:50 and where the ratio of2-hydroxyethyl methacrylate and methyl methacrylate ranges from about1:3 to about 1:50.
 30. The electrochromic device according to claim 11,wherein said cooperative interaction between said free standing gel andsaid front and rear elements makes said device resistant to bending andbreaking.
 31. The electrochromic device according to claim 11, furthercomprising polymeric beads disposed within said chamber.
 32. Theelectrochromic device according to claim 31, wherein said beads comprisea material that will dissolve within an electrochromic device at ambientor near-ambient temperatures within about 24 hours.
 33. Theelectrochromic device according to claim 32, wherein said beads comprisea copolymer selected from the group consisting of: MMA/methacrylic acid,MMA/ethylacrylate, MMA/n-butylacrylate, and poly(propylene carbonate).34. The electrochromic device according to claim 32, wherein said beadsdo not impart any refractive imperfections to said device.
 35. Theelectrochromic device according to claim 11, wherein said layer oftransparent conductive material disposed on said rear surface of saidfront element is a multi-layer stack having a first layer with a highrefractive index, a second layer with a low refractive index and a thirdlayer with a high refractive index.